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Atmosphere 2017, 8(1), 13; doi:10.3390/atmos8010013

Water Tank Experiments on Stratified Flow over Double Mountain-Shaped Obstacles at High-Reynolds Number

1
Institute of Atmospheric and Cryospheric Sciences, University of Innsbruck, 6020 Innsbruck, Austria
2
University of Vienna, Department of Meteorology and Geophysics, 1090 Vienna, Austria
3
CNRM, UMR 3589, Météo-France/CNRS, 31100 Toulouse, France
4
Kjeller Vindteknikk, 2027 Kjeller, Norway
5
Meteorological and Hydrological Service, Zagreb 10000, Croatia
6
Institute of Meteorology and Climatology, Leibniz Universität Hannover, 30419 Hannover, Germany
7
MeteoServe GmbH, 1220 Vienna, Austria
8
National Center for Atmospheric Research, Boulder, CO 80301, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Robert Talbot
Received: 7 November 2016 / Revised: 23 December 2016 / Accepted: 10 January 2017 / Published: 13 January 2017
(This article belongs to the Special Issue Atmospheric Gravity Waves)
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Abstract

In this article, we present an overview of the HyIV-CNRS-SecORo (Hydralab IV-CNRS-Secondary Orography and Rotors Experiments) laboratory experiments carried out in the CNRM (Centre National de Recherches Météorologiques) large stratified water flume. The experiments were designed to systematically study the influence of double obstacles on stably stratified flow. The experimental set-up consists of a two-layer flow in the water tank, with a lower neutral and an upper stable layer separated by a sharp density discontinuity. This type of layering over terrain is known to be conducive to a variety of possible responses in the atmosphere, from hydraulic jumps to lee waves and highly turbulent rotors. In each experiment, obstacles were towed through the tank at a constant speed. The towing speed and the size of the tank allowed high Reynolds-number flow similar to the atmosphere. Here, we present the experimental design, together with an overview of laboratory experiments conducted and their results. We develop a regime diagram for flow over single and double obstacles and examine the parameter space where the secondary obstacle has the largest influence on the flow. Trapped lee waves, rotors, hydraulic jumps, lee-wave interference and flushing of the valley atmosphere are successfully reproduced in the stratified water tank. Obstacle height and ridge separation distance are shown to control lee-wave interference. Results, however, differ partially from previous findings on the flow over double ridges reported in the literature due to the presence of nonlinearities and possible differences in the boundary layer structure. The secondary obstacle also influences the transition between different flow regimes and makes trapped lee waves possible for higher Froude numbers than expected for an isolated obstacle. View Full-Text
Keywords: laboratory experiments; lee-wave interference; mountain waves; rotors; stratified flows; valley flushing laboratory experiments; lee-wave interference; mountain waves; rotors; stratified flows; valley flushing
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Stiperski, I.; Serafin, S.; Paci, A.; Ágústsson, H.; Belleudy, A.; Calmer, R.; Horvath, K.; Knigge, C.; Sachsperger, J.; Strauss, L.; Grubišić, V. Water Tank Experiments on Stratified Flow over Double Mountain-Shaped Obstacles at High-Reynolds Number. Atmosphere 2017, 8, 13.

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